Synthetic Iron-Sulfur Clusters for Understanding the Roles of Heterometals in the Nitrogenase Cofactors

With the support of the Chemical Synthesis program in the Division of Chemistry, Professor Daniel Suess of the Massachusetts Institute of Technology will study how to efficiently convert atmospheric nitrogen into ammonia and other substances that can be used as fertilizer. Currently, this is done using the Haber-Bosch process that is both energy intensive and generates about 2-3% of the annual carbon dioxide emissions world wide. In contrast, naturally occurring enzymes, called nitrogenases, can perform this goal at room temperature without the formation of carbon dioxide. This project will utilize the knowledge of these enzymes to design small molecules that exhibit nitrogenase activity. This will reveal the fundamental chemical bonding that underlies efficient nitrogen activation and provide a blueprint for the design of catalysts for nitrogen fixation. The research will enhance our understanding of the natural world, particularly the roles of nitrogenases in the global nitrogen cycle and our ability to provide the fertilizer needed to support food productions. In educational and outreach activities, the Suess lab will host local high school students as interns, engaging them in the research activities and more generally in the process of scientific discovery; and mentor elementary-school girls, helping to cultivate their interest in STEM disciplines. The project will utilize synthetic chemistry to understand why the Mo, V, and Fe-only nitrogenases show different proclivities for productive dinitrogen reduction. Specifically, the bonding in synthetically versatile, cubane-type [MFe3S4] model clusters and electronically simplified variants thereof that are more tractable for analyzing M–Fe bonding will be studied. An objective is to determine how the composition of the cluster affects the strength of the M–Fe bonding and how this in turn impacts the cluster’s ability to bind and activate dinitrogen and related substrates; and help rationalize why metal ion doping in heterogeneous catalysts often improves dinitrogen reduction catalysis. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.